As fuel efficiency and emissions concerns become increasingly important, more and more vehicles are being equipped with turbochargers utilizing exhaust gas recirculation (EGR) systems. EGR systems increase the fuel efficiency of an internal combustion (IC) engine and reduce the emissions of noxious exhaust gases by recirculating a portion of the unused fuel and exhaust gases back to the engine for subsequent use, instead of releasing them into the environment. In a low pressure (LP) EGR system, the exhaust gases are reintroduced to the engine just upstream of the turbocharger compressor, at the turbocharger compressor inlet. At this location, the pressure is low, even under high engine boost conditions. This solves some of the quality issues associated with related high pressure (HP) EGR systems.
As illustrated in FIG. 1, EGR gases are mixed with conventional inlet air just before entering the turbocharger compressor. The ratio of EGR gases to inlet air determines the efficiency of the EGR system and engine overall. The utilization of EGR gases, however, is often limited by the condensation of water droplets in the EGR gases near the mixing point as the hot, humid EGR gases are cooled by the cool, dry inlet air. This cooling usually occurs through (and condensation usually occurs on and adjacent to) the wall that divides the hot, humid EGR gases from the cool, dry inlet air just prior to the mixing point, in the hot, humid EGR gases. This problem is especially pronounced under cold start and low temperature operating conditions, sometimes delaying the normal activation of the EGR system. This can compromise emissions testing results, for example, and otherwise degrade engine performance. In a worst case scenario, under extreme conditions, ice particles can even be formed in the EGR gases, exacerbating these issues.
Problematically, the condensed water droplets (or ice particles) near the mixing point of the EGR gases and the inlet air are fed directly to the turbocharger compressor. These water droplets (or ice particles) can impact the turbocharger compressor wheel, blades, and other components, damaging them. As illustrated in FIG. 2, the water droplets initially exert a force perpendicular to the component surface, which causes a blast wave upon component surface contact, resulting in a force exerted parallel to the component surface. This force exerted parallel to the component surface can impinge upon surface imperfections, causing spalls, cracks, etc. at or near such surface imperfections.
Thus, what is still needed in the art is an EGR system that inhibits the condensation of water droplets and the formation of ice particles near the mixing point of the associated EGR gases and inlet air, and especially on and adjacent to the wall separating the EGR gases from the inlet air, such that the subsequent turbocharger compressor wheel, blades, and other components are not damaged by the condensed water droplets or formed ice particles. One way this can be done is through the selective high temperature (HT) circuit heating of low temperature (LT) circuit components (e.g., the water-cooled charge air cooler (WCAC), compressor, selective catalytic reducer (SCR), etc.) that are normally cooled by the LT circuit before starting the LP EGR in certain cold cycles. This circuit shifting can be controlled by an electronic control module (ECM) to target a setpoint temperature that avoids condensation risks at subzero conditions, for example.